The invention relates to a motor vehicle with a pneumatic leveling unit operated by a compressor to control the level of vehicle under varying loads. The loading unit is located between the axle and the chassis of the vehicle and under the action of compressed air can be operated to change the distance between the chassis and axle to maintain a desired level.
It is not desirable for the pneumatic leveling unit to be de-activated when the vehicle is not in operation. Otherwise, the vehicle may, when loaded, subside until it comes to rest on the rubber cushions. This results in poor riding comfort on starting out until the desired level position has been reached after the vehicle has started out and the compressor has been activated.
On the other hand, constant supply of voltage to the compressor by the battery is questionable, inasmuch as this can result in premature depletion of the battery.
One object of the invention is to assure adequate riding comfort in the start-up phase of the vehicle with a series-produced motor vehicle without unduly draining the battery charge.
This is accomplished in the invention by using a system where the compressor undertakes to raise the vehicle above a minimum level limit only when the trunk compartment is opened. Thus, when the engine is not running there would be no drain on the battery until the trunk lid is moved to an open position. The battery would then provide sufficient power until the trunk lid is closed or the desired minimum level is reached.
Inhibition of the undesirable condition in which loading of the trunk compartment, in particular, leads to extreme subsidence of the rear of the motor vehicle until it comes to rest on the rear rubber cushions is to be regarded as an advantage of the invention. Only as a result of entry of passengers is a vehicle loaded in such a way that the load is distributed to some extent equally between the two axles, so that such abrupt subsidence is not to be feared. Hence compressor operation is permitted for a limited time, against the event that a minimum level limit has been reached or exceeded.
It is provided in a preferred embodiment of the invention that opening of the trunk lid is sensed by the trunk switch monitor which activates the trunk light. This switch can be used simultaneously for sensing an open trunk and corresponding actuation of the compressor.
In one embodiment the compressor remains constantly actuated as long as the trunk is open. A somewhat more expensive alternative provides that when the trunk is opened, the compressor may be activated only for a prescribed period of time determined by a time function element which is installed in an electronic system. When the trunk is opened and this latter system switches the compressor off after a specific period, regardless of whether the trunk is open or closed.